Apparatus and method for mixing and pumping fluid explosive compositions

ABSTRACT

A RELATIVELY SMALL, MOBLE SYSTEM FOR MIXING AND PUMPING SLURRY EXPLOSIVES INCLUDES A VEHICLE AND DEMOUNTABLE UNITIZED EQUIPEMENT FOR METERING, MIXING AND PUMPING TO A POINT OF USE, A SLURRY OF LIQUID AND NON-DISSOLVED SOLID PARTICULATE INGREDIENTS. THE PRODUCT IS A SUSPENSION OF PARTICLES IN A LIQUID MEDIUM OF VISCOUS GEL FORM. APPARATUS INCLUDES MULTIPLE SUPPLY SOURCES AND FEEDERS FOR PARTICULATE INGREDIENTS AND A PUMP FOR LIQUID, ALL EMPTYING INTO A MIXING ZONE, THE INDIVIDUAL FEEDERS BEING DRIVEN AT SELECTIVELY OR VARIABLY CONTROLLED RATES. OPERATION OF THE FEEDER ELEMENTS MAY BE MECHANICAL OR BY FLUID PRESSURE. THE DESIRED VOLUME OF LIQUID IS ADJUSTABLE, BEING METERED BY MECHANICAL PUMP AND/ORTIMER MEANS, PRODCUT SLURRY DELIVERY IS BY A VARIABLE OUTPUT PUMP. THE SYSTEM IS DESIGNED TO CARRY THE SEPARATE INGREDIENTS SAFELY TO SITES OFTEN INACCESSIBLE TO PRIOR ART EQUIPMENT, THERE TO PREPARED THE EXPLOSIVE SLURRY OR GEL ON SITE AND DELIVER IT PROMPTLY TO THE POINT OF USE, WHETHER ON MOUNTAIN SIDES OR IN UNDERGROUND TUNNELS, EXCAVATIONS, ETC.

Oct. 5, 1971 c. E. CHRISTENSEN ETAL 3,610,088

APPARATUS AND METHOD FOR MIXING AND PUMPING FLUID EXPLOSIVE COMPOSITIONS died May 51, 1968 4 Shets-Shefl 1 I i l 1 i a i 1 l i: I 1 l I ax/o/zz-w lsawrxaul 72M? 1 I H i I l 30 l I i i i :5 ENG/NE I L] l -39 a I: INVENTORS 23 #05527 a. cur

641?) M- THOIPMLEY 6; Z CAL WM 4'. mien-W35 ATTORNEY 1971 c. E. CHRISTENSEN EI'AL I APPARATUS AND METHOD FOR MIXING AND PUMPING FLUID EXPLOSIVE COMPOSITIONS 4 Sheets-Sheet 1';

Filed May 51, 1968 511971 c. E. CHRISTENSEN ETAL 3,610,088

APPARATUS AND METHOD FOR MIXING AND PUMPING FLUID EXPLOSIVE COMPOSITIONS Filed May 31, 1968 4 Sheets-Sheet I5 Oct. 5, 1971 c. E. CHRISTENSEN ETAL 3,610,088 1 APPARATUS AND METHOD FOR MIXING AND ?UMPIN G 1 FLUID EXPLOSIVE COMPOSITIONS 1 Filed May 31, 1958 4 Sheets-Sheet 4.

SOLUTION TANK United States Patent Oflice APPARATUS AND METHOD FOR MIXING AND PUMPING FLUID EXPLOSIV E COMPOSITIONS Calvin E. Christensen, Salt Lake City, and Robert B. Clay and Gary M. Thornley, Bountiful, Utah, assignors i Intermountain Research and Engineering Company,

Filed May 31, 1968, Ser. No. 733,707

Int. Cl. F42b 3/00; C06b 21/02 Us. 01. 8620 21 Claims ABSTRACT OF THE DISCLOSURE A relatively small, mobile system for mixing and pumping slurry explosives includes a vehicle and demountable unitized equipment for metering, mixing and pumping to a point of use, a slurry of liquid and non-dissolved solid particulate ingredients. The product is a suspension of particles in a liquid medium of viscous gel form. Apparatus includes multiple supply sources and feeders for particulate ingredients and a pump for liquid, all emptying into a mixing zone, the individual feeders being driven BACKGROUND AND PRIOR ART In U.S. Pat. No. 3,303,738 to Clay et 211., issued Feb. 14, 1967, a method is disclosed and claimed for mixing and pumping slurry explosive. This method has revolutionized explosive preparation and placement for large outdoor blasting operations. As described in said patent, a blasting agent is prepared by blending liquid and solid ingredients into a viscous gel or slurry which can be pumped to a borehole, etc., through a delivery hose or tube. Compositions are of low viscosity when pumped but become thickened further ,as soon as or immediately after they are pumped. This prevents gravitation segregation of the suspended solid ingredients from the liquid menstruum or their elution by ground Water, etc., when the composition sets or becomes quiescent in the borehole. Facilities for storing, feeding, mixing and pumping have been combined on a large mobile vehicle which carries a large supply of a liquid ingredient, usually an aqueous solution of ammonium nitrate or similar oxidizer salt, and carries also supplies of one or more dry ingredients which are to be mixed with and suspended (or sometimes partly dissolved) in said liquid in formation of the explosive slurry. Means are known whereby the composition of the explosive being prepared may be varied by changing proportions from time to time of one or more of the ingredients. The mix may be changed during a single and continuous operation of loading or filling a single borehole, if desired.

The apparatus and method mentioned above has been successful commercially but has not been entirely suitable for some other types of mining and construction operations, e.g., operation on narrow ledges, in underground mining operations, etc., for several reasons. In some cases the prior apparatus is too large for use in narrow quarters or where overhead clearance is limited. The prior system uses some complex mechanical units and electrical controls which are unnecessarily complex for smaller operations, particularly in places of difiicult access.

Patented Oct. 5, 1971 One object of the present invention is to make it possible to extend to smaller and much less accessible :operations most of the benefits of the'larger automatic orr-site mixing-pumper type operation described above.

By use of simple mechanical and/or fluid operated controls, and by a convenient arrangement of the essential operating elements, storage bins, tanks, and means by which the several ingredients are dispensed and blended, a highly versatile but economical and convenient system has now been designed.

Another object isto simplify an explosive and pumping system which includes most of the essentialfeatures mentioned above but uses basically simple and accurately controllable means to bring solids and liquids together. It includes means for reducing explosion and other hazards.

In lieu of strictly mechanical controls and drives, the present invention also includes, as alternatives, fluid operated controls and/or drive means for the various functions, including means for driving all the essential elements from a single central fluid power unit. The controls and/ or the drives may be operated by either pneumatic or hydraulic means.

Thus the new system appears to have several advantages over equipment of the prior art, being adaptable for more types of use and suitable to replace the former equipment even in large scale operations, in many cases.

All the above and other advantages will be more apparent as a detailed description of the method and apparatus are given.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a system typical of the present invention as mounted on a small or conventional pickup" truck.

FIG. 2 is a larger side view, partly in section and with certain parts broken away, showing the mechanical drive means and controls by which the ingredients are combined to form a slurry and then pumped to a point of use.

FIG. 3 is an end view at the rear of the vehicle, which may be considered the front of the mixer-pumper unit, including a modified mixer.

FIG. 4 is a view (from the rear of the vehicle) with parts removed to show arrangement of the slurry mixing and pumping components, including some of the controls, etc.

FIG. 5 is an elevational view at the rear of the mixer pumper unit, i.e. looking to the rear from the vehicle cab from approximately line 5--5 of FIG. 1.

FIG. 6 is a diagrammatic plan view showing approximate relative location of some of the major components of the system.

FIG. 7 is a larger and fragmentary plan view, with some parts in section and some broken away to show the drive and feed mechanism for particulate solid ingredients.

FIG. 8 is a fragmentary vertical section taken approximately on line 8-8 of FIG. 7.

FIG. 9 is a diagrammatic view of an alternative system wherein the various operating components are operated by fluid power.

FIG. 10 is a partial elevational view, with some parts in section, showing a modified mixing system for combining a liquid and dry particulate ingredients.

FIG. 11 is a front view of the apparatus of FIG. 10.

DESCRIPTION OF PREFERRED EMBODIMENTS The apparatus and method of the present invention have, in general, the same advantages, and others in addition, as those described in the above mentioned patent. They eliminate need for a separate mixing plant; they reduce the cost and greatly decrease the danger of transporting blasting materials to places where they are to be used,

which are often difiicultly accessible'and typically have poor roads. The need of packaging the explosive for handling is obviated, although packaging still may be done for special situations, if desired.

The apparatus of this invention may, in fact, be used for mixing and packaging, if desired. There are considerable reductions in manpower requirements, which would otherwise be necessary to load the explosive into boreholes and other points of use.

In its method aspects, the invention contemplates the use of an aqueous or partly aqueous solution of ammonium nitrate or the like, along with various sensitizers of known types, such as particulate aluminum or other heat producing metals which are essentially non-explosive per sc. Other fuels are usually added, such as carbonaceous materials, sulfur, and other ingredients as is now well understood in the art. Thickening agents to control the viscosity of the blasting agents are normally added in small proportions, suitable for their purpose. In general, the materials, liquid and solid, are mixed together to form at first a relatively non-viscous mass or slurry which can still be pumped through a delivery hose or pipe without excessive pressure or power requirements. The thickening ingredients, or some of them, preferably are so chosen and their addition to the mixture is so timed that while the blasting agent can still readily be pumped or flowed into place, approximately by the time it reaches there it solidifies or stiifens up sufficiently that there is no separation, or

' essentially no segregation of solids from the liquid menstruum in which they are suspended. In general, these procedures are described and claimed in US. Pat. No. 3,303,73 8, mentioned above, apparatus features being separately claimed in a pending application, Ser. No. 569,993, filed Aug. 3, 1966 now Pat. No. 3,380,333.

Some of the improvements in method aspects of the present invention over those previously described relate to use of simple unitary mechanical or fluid drives and controls, improvements in effective mixing and greater facility for production of individual or sequential batches, which in some cases may be started or stopped, or even 7 their composition changed at will during filling of a particular borehole. Also, the degree of aeration which can be incorporated into the explosive, when such is desired, may be varied widely and by very simple control manipulations.

Referring now in detail to the drawings, FIG. 1 shows a simplified mixing and pumping system, a presently preferred form of the present invention which is mounted on a truck 11 which may be of any conventional style, having a cargo space 13 in which the assembled unit 15 may be mounted bodily. The unit normally is not secured permanently to the truck, although it can be, but it is ordinarily independent and is readily unfastened, if secured at all, so that it may be lifted out bodily and placed on the ground or on some other mobile supporting apparatus such as a mine car. The latter may be needed for use in mine tunnels where overhead clearance would not be sufiicient for a vehicle of larger dimensions. This whole unit 15 comprises a generally rectangular framework 17 of conventional type, which need not be described in detail. The

unit has a main base or floor 21, supported on rails 23 or equivalent. See FIG. 2. The unit or system of FIGS. 1 and 2 comprises a drive motor, e.g. a gasoline engine 25 mounted in the front right corner of the cargo compartment of the vehicle. Obviously, for some situations an electric motor or a fluid motor may be used in lieu of engine 25.

For convenient reference hereinafter the rear end of the truck or vehicle may be considered the front of the slurry mixing and pumping unit, since that is the place where it is controlled primarily. In this sense, the motor 25 is located in the rear right corner as one faces the unit. This motor is equipped with a fuel tank 27 and on its power shaft 28 is mounted a triple drive pulley 29. An air compressor 37 is located near the rear left corner. The front sheave 30 of pulley 29 is connected by a belt 31 to a pulley 33 on the drive shaft 35 of the air compressor unit 37. See FIG. 5. The latter is mounted on a suitable base 39 and is provided with an intake air filter 41, a main outlet line 43, and a pressure control line 45. The latter operates automatically to open a by-pass valve in the compressor and stop air delivery; such is known in the art and forms no part of the present invention. For example, when the air pressure in the air receiving tank 49 reaches a predetermined level, say 100 lbs. per square inch, through the control line 45 the compressor is rendered inoperative. When the pressure in tank 49 drops to a predetermined level, say or pounds per square inch, the compressor will be reactivated.

It will be understood that the motor 25 normally operates more or less continuously. The two remaining inner sheaves of the motor pulley 29 drive a main transmission shaft 51, through twin belts 53 and 55, and double pulleys 56 FIGS. 2 and 5. Shaft 51 is mounted in appropriate bearings 57, 59 and 61, and extends towards the front of the unit, that is, towards the back of the truck; its front end is seen at the left of FIG. 2. Shaft 51 carries a clutch mechanism 71 on which is supported a double belt pulley 73. Clutch operating control lever 75 is pivoted on a stationary member at 77 and is operable by a pull rod 79, equipped with a handle 81, which projects through the cover plate 83. See also FIGS. 3 and 4. When the clutch is engaged, the double pulley 73, through drive belts 87, FIG. 2, drives a pulley 89 mounted on the drive shaft 91 of a slurry pump 93. The latter is preferably of the positive displacement type, receiving slurry through a line 95 equipped with a quick release coupling 97 from a slurry mixing unit 99, which will be described more fully hereinafter.

The slurry pump shaft 91 is provided also with an additional pulley or sheave 103 which through belt '105 drives a variable split pulley 107 mounted on a jack shaft 109. The latter is fixed to the shaft 109 to which also is secured another pulley 111. Pulley 111, through a drive belt 113, drives a floating pulley mounted for free rotation on shaft 117 which is also the operating shaft for a solution pump 119 to be described more fully hereinafter. Pulley 115 has a second sheave 116 which through a twisted belt 118, FIG. 4, drives a pulley 120 fixed to the upper end of a mixer shaft 122 mounted in the mixer unit 99. The mixing operation will be described more fully presently.

The shaft 117 which drives the solution pump 119 is actually driven through a clutch 133 operated by a lever 134, the lever being pivoted at 135 and equipped with a pull rod 136 of which the operating knob or handle 137 extends through the front plate 83. See FIGS. 3 and 4. When clutch 133 is engaged, a dual drive pulley 140 is operatively connected to shaft 117. This pulley is driven by a pair of belts 141, engaged by dual drive pulley 142 on the main shaft 51, to operate the pump. A suction line 121, through which the oxidizer solution is removed from the oxidizer tank 123, extends from the pump inlet almost to the bottom of the oxidizer tank. This tank 123 occupies a major central area of the lower part of unit 15. It normally contains a heated and substantially saturated solution of a strong inorganic oxidizer salt, preferably ammonium nitrate or ammonium nitrate mixed with sodium nitrate, although other oxidizers may be used with or in lieu of ammonium nitrate and/or sodium nitrate, such as calcium nitrate, barum nitrate, etc., or one or more of the various ammonium and alkali metal chlorates and/or perchlorates. The latter may be used singly or in combination with any of the other oxidizers mentioned. The present practice commonly is to use a strong aqueous solution, usually heated, containing from about 60 to 85% by weight of ammonium nitrate, or a mixture of ammonium nitrate and sodium nitrate at or near saturation in warm or hot water.

The pump 119 delivers the solution through its outlet line 147 to the mixing chamber 99, the outlet 260 as shown in FIG. 4 being between the outlets of two augers, described hereinafter, which deliver particulate solid materials to the same mixing chamber.

The main drive shaft 51 operates the main slurry pump 93. Through the pulley 103 and drive belt 105 power is transmitted also to pulley 107, which is connected directly with pulley 111 to drive the floating pulley 115 whenever the slurry pump is operating. The latter, through pulley 116-, belt 118, and pulley 120 drives the mixer shaft 122, whether the pump shaft 117 is rotating or not. The double pulley 142, also mounted on shaft 51 and fixed thereto, drives pulley 140 and the latter drives pump shaft 117. Thus the solution pump does not operate unless its clutch is engaged. In this manner, means are provided for drawing the liquid solution, which preferably is heated as mentioned above, from its tank 123, forcing it into the mixing chamber. Cold solution may be used in some cases. The liquid in the mixing chamber is blended with other ingredients, usually dry and usually including at least some insoluble particles which are to be suspended in the liquid to form a smooth, homogeneous slurry. The resulting slurry finally is pumped by pump 93 from the mixer to the point of use, as will be described more fully. Pump 93 does not operate unless clutch 71 is engaged. However, when it does operate the mixer shaft 122 is rotated too. This helps to prevent building up of deposits in the mixer which might clog the slurry pump or cause other difficulties.

At its rear end, in addition to the double pulley 56 driven directly by belts 53 and 55, the main drive shaft 51 carries an additional pulley 151. This is shown at the extreme right in FIG. 2 and at the upper left in FIG. 5. Through belt 153 pulley 151 drives the input shaft 155 of a gear reducer 157 through pulley 159. This gear reducer may be of a fixed ratio type or it may contain or comprise a variable ratio drive. Its purpose is to provide reduced rotational speed for driving augers which are used to feed dry particulate materials. -In some cases alternative particle feeders such as vibrators or shakers may be used. Through its output shaft 192 pulleys and belts 163, see FIG. 7, the gear reducer drives an anger operating pulley 165, FIG. 7, provided its operating clutch 196, on shaft 192, is engaged. The pulley 165 is mounted on the operating shaft 167 of an anger 169 which is mounted in and extends transversely of the bottom of a hopper or bin 170 adapted to hold a particulate solid, e.g. a supply of auxiliary oxidizer in dry or granular form, such as ammonium nitrate, sodium nitrate, or other particulate oxidizer material. A bin 171, usually but not necessarily larger than 170, is mounted beside the latter and is designated to hold a so-called pre-mix of dry particulate non-oxidizing ingredients to be added to the liquid in making the slurry. This premix contains fuels and/or sensitizers, such as finely divided coal, sulfur, aluminum granules or powder, sugar, etc. It may also contain insensitive particles of self-explosive such as TNT, smokeless powder, etc. Auger 169 feeds materials from bin 17 0 through a tunnel or housing 173 extending below bin 171 and into mixer 99. Auger 180 feeds its ingredients through housing 181 into the mixing chamber or funnel 99. Both auger drive shafts extend to the left, as seen in FIG. 7.

It is obviously preferable for safety reasons not to pre-mix dry oxidizer materials with combustibles such as fuel, carbon, solid hydrocarbons, metallic aluminum, self-explosives, and other fuel materials; hence separate bins and augers are used. The dry pre-mix ingredients may and commonly do include a thickening agent, such as guar gum, starch or equivalent, for increasing the viscosity of the slurry and causing it to thicken or set up, at least in the borehole, so that the suspended solid particles in the slurry will not settle out and cause a failure to detonate when the explosion is desired. However, the thickener, or part of it, may be pre-incorporated in the oxidizer solution or may be added thereto as the solution flows to the mixer and before the liquid is mixed with the dry ingredients. By dry, it is not intended I to mean that the particles are completely dehydrated, although they may be in some cases.

FIG. 8, at the top, shows a fragmentary view of the bin and auger arrangement. Auger is on shaft 182 which passes through bin 170, preferably inside a housing 183, although the shaft can be left exposed in bin 170, if desired. A sprocket'187 fixed to shaft 182 is driven by a chain 188 passing over a sprocket 189 on shaft 167. Thus the two angers 169 and 180 are driven simultaneously, but not necessarily at the same rates to discharge simultaneously the pre-mix or fuel ingredients from hopper 171 and to discharge the so-called drys, which are commonly supplemental oxidizer materials, from hopper 170. The relative discharge rates of the two angers depends on their diameters and pitches as Well as on their rates of rotation. These elements are selected or varied, as desired, to obtain the appropriate proportions of ingredients. Also, the feed rate of both may be changed by changing the drive ratio in the speed reducer 157. Relative rates of either auger may be varied independently also, as by changing one or both sprockets 187, 189, FIGS. 5, 7. By any of these means the appropriate proportions of the various ingredients for a desired formula may be fed, as will be obvious. The effective drive ratios may be changed between batches or even during a single batch or borehole filling operation, if desired. The latter can be done to alter the composition of the explosive slurry while a single charge is being delivered. For example, a more powerful charge may be needed at the bottom of a borehole than higher up and a suitable shift in feed ratios of the respective ingredients will accomplish this objective. When this is desired, a change gear or variable speed drive for one or more feeders should be used, rather than changing sprockets, as is obvious.

As shown in FIGS. 5 and 7 the speed reducer 157 is mounted on shaft 192 which may be its output shaft and which is appropriately supported for rotation in bearings 190 and 191, mounted on a suitable frame member 195. Power input, as already noted, is from pulley 151 through belt 153, FIG. 5.

The output shaft 192 of the gear reducer 157 has affixed thereto drive clutch element 196, designed in this instance for engagement and disengagement by fluid pressure, i.e. an air piston and cylinder assembly of obvious type located inside a housing 197. The latter is operated by compressed air under control of manually operable valve 200, from tank 49. The air connection is indicated in FIG. 7 at 198. The pivoted control lever 199 of a valve operating control unit 200 is mounted in the upper left side of the control panel, as shown in FIG. 3. By this means the clutch may be engaged and disengaged with respect to the double output pulley 161. The latter drives belts 163 which engage driven auger pulley 165, as already described.

As best shown in FIG. 4, the mixing unit 99 comprises a tank or funnel member 215, cylindrical in shape at the upper part, but having a tapered or conical bottom portion 216 which connects to an outlet line 217. The latter connects to the slurry pump connection 95, previously described.

The drive shaft of the mixer has mounted on it near the top of cylindrical part 215 a fan or blower 218 which is adapted to draw off dust from the upper part of the mixing chamber through an opening 219 provided in a transverse partition 220. This is particularly needed when the mix contains very finely divided particles, such as paint grade aluminum, powder, very fine ground gilsonite or coal, etc. An outlet line 221 leads the dust out of the unit and away from the operating mechanism, as shown best in FIG. 3. By this means the mixing chamber is kep t fairly clear so that the operator can observe what is going on, e.g. through the open door 263, also in order that accumulations of explosive materials or otherwise objectionable dusts within the mechanism may be prevented. It will be understood, of course, that the full amount of dust so drawn off is quite small, usually inconsequential. The augers 169 and 180 preferably are arranged to deliver the dry products into the mixing chamber together. During a major part of its operation, the system delivers both liquid and dry particles to the mixer. However, it is often desirable to start one ingredient, usually the liquid, before the dry particulate materials are fed to the mixer.

Shaft 122 of the mixer is mounted in bearings 227, 228, secured to partition 220, and on its lower portions this shaft supports mixing elements 229 and 230 which are of conventional type, e.g. of propeller shape. The lower mixer blade is located in the conical part of the mixing chamber and is made somewhat smaller than the upper one. By these means the ingredients, liquid and suspendable particles, are thoroughly mixed together so that a homogeneous slurry is produced before the mixture leaves the mixing chamber. It flows by gravity through the outlet 217 and proceeds through the quick detachable hose 95 to the slurry pump '93. Some of the particulate solids, such as oridizer salt or gum, may dissolve in the liquid during mixing but at least some of them, such as aluminum par ticles, carbonaceous particles, sulfur, etc., do not.

Supplemental mixing often may be desirable, e.g. to increase slurry sensitivity by aeration, reducing its density, or to improve homogeneity. FIG. 3 shows a pug mill type mixer extension where the mixer 99 has a cylindrical lower end 231 provided with inwardly directed fingers 232, arranged in staggered relationship with respect to mixing bars 233 on shaft 122. The structure mixes the slurry longer and more vigorously to incorporate fine air bubbles and it can reduce slurry density as much as 25% or more by aeration. With some formulations also, it gives time for the thickener to become more effective. Slurry outlet hose 95A, FIG. 3, is shorter than hose 95, FIG. 4, because of the longer mixing zone.

The slurry pump 93 which is driven as previously described, is preferably a positive displacement pump. It is designed to propel the slurry at an adequate rate, say 50 to 500 pounds per minute, through a delivery hose or conduit 238 connected to outlet 236 through a three-way valve 235 which is provided in the outlet line 236 from the slurry pump. Valve 235 has a control handle 237 and is arranged so that when the delivery valve is wide open the whole pumped stream may pass to the borehole through the outlet 238. Alternatively, a part of the stream, or all of it, for that matter, may be recycled to an appropriate point, as the pump inlet, through a bypass or recycle line 239', depending on the valve setting. The valve can also be closed to provide for blow-down or expulsion of residual slurry in the hose line. In lieu of the three-Way valve shown, two separate valves of ordinary design may be used. The two valves, of course, may be interconnected to a single control. By either arrangement it will be understood that some or all of the mixed slurry can be recycled through line 239 to the pump, or to the mixing chamber above it, if desired, to control the slurry level therein by merely pushing the lever 237, FIG. 4, to the appropriate control position. In this way, although the pump is operating at capacity and the slurry is flowing through it, the valve may be set so that no slurry flows to the borehole until the valve is moved to the slurry flow position. The valve thus controls slurry level in the mixer, and this level can be observed by the operator, either by watching sight glass 240* which contains a visible fluid to indicate slurry level by manometer pressure, or by observing the slurry level directl through open door 263, FIG. 4. By appropriate valve setting it can all be recycled, or it can all be sent to the delivery point. When slurry pump 9.3 is not operating, the valve 235 can be closed so that air pressure can be admitted through blow-down line 241, under control of a valve 282 to clear residual slurry from the delivery hose. The slurry pressure is indicated by a gauge 243.

It will be understood, of course, that a hose, or a pipe if desired, of suitable length and diameter is used to conduct the slurry from the pump to the borehole or to packaging, or to any other intended place of use or delivery. The hose or pipe should be large enough to deliver, without undesirable high pressure, a stream produced as fast as ingredients fed to the mixer requires. It should not be so large, however, as to allow significant separation or stratification of solid particles from suspension in the mix. The machine may be used either to fill boreholes, etc., or to package slurry in suitable receptacles; in the latter case the hose is simply led to an appropriate receptacle filling point. If desired, a flow meter may be included in the delivery line to show directly the quantities delivered.

A water tank 250 is included in the system so that a supply of clean water may be available for flushing out valves and flow lines in the equipment, rinsing out the mixer, and cleaning hoses and other internal or external parts, as desired. One arrangement is to fit the water tank under one of the sloping sides of the solids hoppers or bins 170, 171. See FIG. 8. Another arrangement is to mount the water tank 250A, as in FIG. 6, inside the solution tank 123. With the latter arrangement the hot solution, which is customarily used, will keep the water hot. See FIGS. 2 and 8, as well as FIG. 6. A water outlet line 251 extends to or near the bottom of the tank 250A, FIG. 2, and leads to a valve 252 for a flushing hose 255, FIGS. 3 and 6. The latter can be used to rinse the mixer, wash off the apparatus, etc. Water is forced out by maintaining air pressure in the tank 250A, supplied through a line 356 to the top of the tank from air pressure tank 49. This pressure may be of any suitable magnitude, say lbs. per sq. inch, more or less, to force the water at effective pressure through outlet line 251 when valve 252 is opened. A control valve 254 is provided for draining the solution tank. Hose 253 can be connected to pumps 93, in place of connector 95A, for flushing out the pump, hoses and other connected parts.

In a typical operation, the oxidizer solution temperature maybe kept in insulated tank 123 at a temperature of up to about 185 F. In this case, hot water of about the same temperature is normally available with the arrangement of FIGS. 2 and 6. With the arrangement of FIG. 8, more capacity for liquid solution is available in tank 123 but the triangular cross-sectioned tank is not as suitable for elevated pressures. Water may be drawn by gravity into a small unpressured tank, not shown, which then can be pressurized with air and used for flushing, etc. When it is desired to refill the water tank in either case, the air pressure is relieved by closing an air supply valve and opening a suitable vent, not shown. Then water can then be run in from a suitable water supply by reverse flow, e.g. through the hose 255 and valve 252, etc.

As shown in FIGS. 4 and 7, the solution normally is fed into the mixer 99 through line 147 (see also FIG. 8), outlet 260, which is placed between the outlets of the augers 169 and see FIG. 4, in dotted lines behind shaft 122. The outlet 260 can be in the form of a simple pipe end or a spray nozzle. The latter can discharge a flow of sufficient width to cover the falling dry particles as they emerge from the augers and facilitates mixing. In either case the dry particles are wetted and washed down the walls of the mixing tank 215. The inspection door 263, is hinged at 262, on the front of the mixer tank as shown in FIG. 4.

The system normally will be calibrated so that a counting device 280 records an appropriate factor, e.g. the revolutions of anger 180 in the pre-mix bin 171. The connections are shown from a pulley 273, on shaft 182, through a belt 274, pulley 275 on jack shaft 276, which has a flexible shaft 277a on its front end to drive the counters. Each revolution of shaft 182 will deliver a certain specific quantity of pre-mix solids; the other ingredients will be fed in appropriate proportions for each mix. The slurry so-produced is caught, weighed and the counting device calibrated to determine quantity of slurry delivered per unit count. Counter 280' is of the resettable type. A counter 281 of the totalizer type, FIG. 3, shows the total quantity of explosive delivered over an extended period of time. For each different mix a new calibration is made, if necessary.

This system has advantages over the prior systems in addition to compactness, simplicity and portability. It is versatile and readily controllable and adjustable in all its functions. For example, the density of the mix produced may be varied and controlled in several ways with or without change in proportions of ingredients, (a) by choice of dry ingredients which promote or control foaming or gas entrapment in the slurry, (b) by forming bubbles or froth in the solution, e.g. at the pump 119 (by cavitation or drawing air into the liquid solution before solids are added, and/or by including a foam stabilizer in the liquid), (c) by introducing gas-forming ingredients, such as carbonates, etc., with the dry ingredients (premix) or by permitting cavitation or air injection (or injection of other gases) at the main slurry pump. The latter, however, must be done with care so as not to introduce large bubbles which might produce discontinuities in a column of explosive or promote slurry instability. The liquid solution itself may contain a small amount of a thickener, such as guar gum, etc., which will stabilize at least the fine gas bubbles, as introduced in any of these ways. This forms no part of the present invention. Finely divided gas bubbles may be incorporated in the liquid before solids are added, i.e. before it reaches the mixing zone. Bubbles may be added in said zone, too, or at the slurry delivery pump, or at both.

Thus the density and sensitivity characteristics of the delivered explosive slurry may be controlled as desired. This can be done entirely without use of detergents or surfactants, or by use of very small quantities of such. This makes it possible, in the filling of a single borehole, to start at the bottom with a dense and relatively gas free slurry having a substantially incompressible and continuous liquid phase. Such slurry has special properties and advantages as pointed out in US. Pat. No. 2,930,685. Later, as filling proceeds, the slurry density may be reduced progressively or in one or more steps so as to place less weight of explosive in each unit volume of borehole. This is often advantageous and economical since the blasting force need not be as great towards the top of the charge. In a broad sense, even these aerated slurries may be considered to have a substantially-continuous liquid phase, so long as aeration is confined to very small bubbles and is not excessive. This system has advantages of simplicity in construction, operation and control.

The prime mover preferred in most cases is a relatively inexpensive single cylinder gasoline engine. Drive of all units is primarily through the single main drive shaft 51 which operates the solution pump 119, the augers 169, 180, the fan or blower 218, the main slurry dispenser pump 93 and the mixer 229, 230, from the latter. The slurry pump, it should be noted, operates at all times so that slurry need not accumulate in the mixer. This is an important safety feature. By opening the slurry outlet valve, the operator can be sure that the system is emptied after the solution and solids delivery means have been closed down. Since the mixer must operate whenever the slurry pump operates, there are no unmixed accumulations in the mixing chamber, another safety feature. The dust removing blower is still another. By the blow-down operation previously described, the hose or other delivery tube can be blown clean and empty.

The air compressor 37, which is an auxiliary in a sense, is driven directly from the engine. It supplies air pressure to operate the various pneumatic controls and to pressurize the water tank for auxiliary liquid supply and/or cleaning. Water from this tank can be added to the mix if desired. The pressurized water supply is another safety feature and, of course, the separation of fuels and oxidizer until mixing and immediatel delivery is the most important safety feature of all.

The several controls may all be pneumatic, for convenience, such as the controls 197 for clutch 196 which drives the augers for feeding the particulate solids.

The air compressor stores compressed air in tank 49 which, as shown in FIG. 5, is mounted in any suitable place, e.g. in the corner behind the vehicle driver in a normal left-hand drive vehicle. The compressor output line 43 leads the top of the tank. Pressure control line 45 has been mentioned above. A filter 352 is shown in the outlet line, followed by a regulator and pressure gauge 353. The latter is followed by a lubricator 354. From the lubricator, the air flows through line 356 and appropriate branches to the various valves and controls already mentioned.

An air pressure chamber is provided in the water tank so that water for rinsing, etc., is available at good pressure. A main air line 358 leads to valve 282, FIG. 4. In this case, as already noted, slurry valve 235 is closed and upon opening valve 282 the air is admitted into line 241 to blow out the slurry in the delivery line without blowing back into the slurry pump or mixing unit, etc. Line 241 contains a check valve to prevent slurry entering the valve 282 and connected parts.

The general operation will now be described. When the unit is started up, the slurry pump is started first of all by engaging clutch 71, i.e. by pulling the handle 81, FIG. 4. Shaft 51 then drives the slurry pump through belts 87, FIG. 2. When this occurs, the mixer and blower mechanism 229, 218, etc., FIG. 4, is driven through belt 105, jack shaft 109, pulley 111, and belt 113. The latter drives floating pulley which is secured to its companion to drive the twisted belt 118, etc.

The mixer is driven whenever the slurry pump operates. Normally, both of these are in operation before any ingredients are fed into the mixing chamber 99. This prevents building up deposits of unmixed materials, either in the mixer or in its outlet line to the slurry pump 93.

The next step, normally, is to start the oxidizer solution which is fed by pump 119 from the supply tank, the solution being drawn into the tank through line 121 and fed to mixing chamber 99 through line 147 and its outlet 260. Activation of clutch 133 through lever 135 and handle 137 initiates this operation.

Next, the augers are started to dispense the dry materials into the mixing chamber. It is usually preferable to start the liquid flow first and stop it after flow of the solids is stopped to prevent building up deposits of granular materials on the wet surfaces of the mixer elements and tank. However, this may not always be necessary. Activation of the pneumatically controlled clutch 196, FIG. 7, starts and stops the augers and this may be done manually. Preferably, however, this control is operated automatically from the liquid supply line, so that the clutch 196 is engaged after liquid starts to flow, as by a pressure build-up in line 147 sensed by elements 361, FIG. 4, which transmits a clutch closing signal through line 362, shown only fragmentarily, to clutch control element 197, FIG. 7.

Normally, the slurry valve 235 will not be opened until a small amount of slurry accumulates above it in slurry pump inlet line 95, FIG. 4 or 95A, FIG. 3, and a small accumulation usually is permitted in the bottom of the mixer. The purpose of this is to prevent cavitation or drawing in large amounts of air into the slurry pump. The by-pass line 239 normally recycles a small proportion of the pumped slurry to the mixer, this proportion being determined by the setting of valve 235 (by control handle 237, FIG. 3 or 4). The by-pass can be connected into the line 95 or 95A, instead of into the mixer, for instance at connection 363, FIG. 4. (The recycle line is not shown in FIG. 3 but is shown in dotted lines in FIG. 4.) It is usually desirable to keep enough slurry in the mixer to keep the mixer blades, or at least the lower ones, covered to avoid poorly mixed slurry products. In fact, the degree of mixing can be increased considerably by increasing the recycled proportion and setting the valve 235 appropriately. This makes it certain that continued flotation of dry ingredients on top of the slurry will not occur to prevent good mixing.

The height of slurry in the mixer is indicated by the sight tube or manometer 240. Some operators prefer to watch the slurry level and the quality of mixing by leaving door 263 open. In this case, a small inward draft caused by blower 218 tends to keep dust from fine dry carbonaceous materials, powdered aluminum, etc., from billowing out to obscure the view and deposit dust on the equipment. Use of the auxiliary mixer elements 231, 232, 233, as shown at the bottom of FIG. 3, makes it unnecessary to do this. However, the solids should be well washed with the liquid, to insure a homogeneous mix, even though some of them may be lyophobic and resist actual wetting.

In pumping the explosive blasting slurry into a borehole, there should not be excessive aeration, although some aeration may be desirable to improve sensitivity. The degree of aeration can be largely controlled by controlling the extent of slurry recycle and controlling slurry level in the mixer. The dry particulate solids bring some air in with them. By performing a folding sort of mixing, obtained by holding the slurry level in the mixing chamber at the right level with respect to the mixing blades, more aeration can be obtained. Aeration can be reduced by adding more liquid to get a smoother softer slurry or by the timing and quantity of solids stirred into a partly prepared slurry.

The delivery hose may contain considerable slurry, especially if it is a long one. It usually is desirable for economic reasons to empty the hose by blow-down, using the compressed air connection and valve 282, as described above, before moving to the next hole or filling operation.

The system described above has the advantages of simplicity, using a single main drive shaft from which motive power is taken off for pumping, dispensing and mixing. It depends on individual controls for the several clutches, etc., to get the desired timing and proportions of ingredients, dispensing, recycling, control of delivery and blow-down. For some purposes, it is desirable to program all these controls and the system shown diagrammatically in FIG. 9 is well suited to such programming or automation.

Referring back to FIG. 3 above, an interleaved blade or finger type mixer 34 of the pug mill type was shown at the bottom of the mixing unit. For some purposes a mixer, as shown in FIG. 10, is preferred, omitting the propeller or paddle type stirrers 229, 230, FIG. 4. Such a unit consists of a mixing chamber or vessel 501, having its longitudinal axis inclined from about 5 to 90 with respect to a horizontal plane. A mixer shaft 502 is mounted axially within the mixing vessel, being driven, for example, by a pulley or equivalent 503 operated by any suitable mechanism, not shown. Inwardly extending from the walls of the vessel towards its center are a series of projecting radial fingers 505, 506, etc. The shaft itself is provided also with a series of radial fingers or blades 509, 510 which move in interleaved fashion between blades 505, 506, in pug mill fashion. The outlet end of the mixing vessel may be closed either by a heavy rubber flap 509. FIG. 11, which resists flow until ahead of slurry builds up, or it may be closed by rotatably adjustable end plate 511, FIG. 10, held in place by a retaining ring or flange 512, and having outlet opening 513 through which the slurry product flows. The amount of slurry inventory kept within the mixing chamber, FIG. 10, and the degree of mixing, aerating, etc., depends on the position of outlet 513. By rotating the plate 511 to the position shown in dotted lines, FIG. 11, a larger inventory may be maintained. When the rubber flap 501, FIG. 11, is used, a spiral impeller or slinger 516, fixed to shaft 502 pro- 12 pels the ingredients towards the outlet end. This prevents wet material from backing up into the inlet 517 through which the dry particulate solids are fed.

The dry solid particles may be supplied by one or more augers, through line 518, as explained above; see FIG. 11. Liquid is drawn or pumped in through line 519. This liquid may be water or water mixed with other liquids or an oxidizer solution in such, as desired. All of the salt may be supplied in dry form. The slurry thus may be prepared from water, salt and the various insoluble particles required, all fed separately into the mixer. It is generally preferred to use pre-dissolved oxidizer, but this is not always necessary with this effective mixing system. Thickeners, which are usually preferred to be prehydrated, may be mixed in by holding the ingredients for adequate hydration time.

The system shown in FIG. 9 is so arranged that the moving parts are driven by fluid pumps. These obtain their operating power from a stream of circulating fluid driven by a master pump system. In this case two master pump M and M are driven respectively by prime movers P and P Each draws a supply of liquid through an inlet line 300 from a vessel 301 to which the fluid is supplied by recirculation through a filter 302. From master pump M the fluid is circulated through line 303 via a relief and return valve 304 connected at 305 with a return line 306. When the master pump is in operation, all of the fluid is recycled through line 305 unless one or more fluid motors described hereinafter are being driven.

A pressure gauge 307 is attached to line 308 which continues from the relief valve 304 to a manifold 309. From the latter, the driving fluid is led by lines 310, 311 and 312 to solenoid operated valves 313, 314, and 315 respectively. The outlet of the latter is provided with a variable orifice valve 316 in line 310. A similar adjustable valve 317 is provided in line 311 and valve 318 in line 312. These lead respectively to fluid motors MP MP and MP The effluent from these motors passes into a manifold 320 from which it returns through line 321 to recycle line 306.

Each of the motors MP MP and MP drives an auger, the three augers being indicated at 323, 324 and 325. Each of these is used to feed a dry particulate ingredient to the funnel or mixing vessel 330. These materials pass respectively through lines indicated diagrammatically at 327, 328 and 329.

Another line 331, connected to manifold 309, conveys the driving fluid to a solenoid operated cut-off valve 335 which is followed by a variable orifice valve 336. The latter controls the flow of fluid to a fluid motor 337 which, through linkage 338, drives a fluid pump 339 which preferably is of positive displacement type. The latter is used to pump a solution of oxidizer, preferably an aqueuous solution of ammonium nitrate, sodium nitrate, etc., from a tank 341 which supplies the solution to a three-way valve 340.

Thus the pump 339 supplies this liquid solution to the funnel 330 to be mixed with the dry ingredients fed by the respective augers 323, 324 and 325. It will be understood that only one or two of the latter may be used at times. By adjustment of the variable orifice valves 316, 317, etc., the driving speed of any of the motors MP and MP etc., may be adjusted to feed the ingredients at the appropriate rate to obtain the desired composition in the mixing vessel 330.

The other master pump M supplies fluid in the same manner as the first master pump to a relief valve 344 from which it may be recycled, when required, through line 345 to line 306. Thus the fluid reenters the filter 302 through a tube on which a line 347 returns it to both supply tanks 301. A screen 348 is provided in each of the vessels 301 to prevent recirculation of foreign matter through the system. Master pump M is used to supply driving fluid for fluid motor MR, which drives the operating shaft 350 in the mixing chamber 330. This shaft is provided with suitable mixing blades 351.

The master pump M also supplies driving fluid through a cut-off solenoid-operated valve 381 and a variable flow valve 382 in a line 383 which connects to the relief valve 344. Thus a variably controllable stream of driving fluid is supplied to fluid motor MP which drives the operating shaft 385 of the slurry pump 386. In this way the velocity of the pump can be controlled. The pump 386 draws slurry from the mixing chamber 330 through a line 387 and delivers it to a manually operated slurry valve 388 in outlet line 389. A pressure gauge 390 is connected to this line to show delivery pressure. Line 389 terminates in a connection for a flexible hose 391 through which the slurry composition may be delivered to a borehole, packaging station, or other point of use.

Driving energy for the mixer shaft 350 is supplied through line 394, under control of a cut-ofl? valve 395 operated by a solenoid and also under control of a variable orifice valve 396 which determines the rate at which the fluid motor MP is to be driven. This motor may be driven at high speed, if desired, to beat air into the slurry and reduce its density, which is sometimes desirable.

An air compressor 410 supplies compressed air through line 411 to an air tank 412 from which it may be withdrawn through line 413. Any suitable motive power may be used for the compressor, such as its own motor or a power take-off. One branch line 414 from the tank outlet leaves the air tank at full pressure to a cut-0E valve 415 and thence through a line 416, to connect with slurry output line 389. Since this line is at full tank pressure, by opening valve 415 manually and closing valve 388 adequate pressure is available to blow-down or clean out the hose 391. This may be required occasionally because of the viscous nature of the slurry which may be in the hose. The check valve 417 prevents blowing slurry back into the pump 386.

Another branch 421 of line 413 goes through a pressure reducing valve 420 in line 421 to a multi-purpose valve 422. Through the latter air may be vented through a line 424 or it may be passed at the desired pressures through a line 423 into a water tank 425. In this way pressure is applied to the water so that it may be forced on through a line 427, under control of a manually operated valve 428, to connect with a hose 429. The latter is used for various purposes such as washing down the apparatus, flushing the mixer, etc.

A branch line 430 also leads from valve 428, which is a. three-way valve, to a manually operated three-way valye 340. By appropriate setting of these valves water may be drawn from the water tank to flush out the pump 339 and/or the mixing vessel 330. Ordinarily, however, valve 340 will be used to draw the hot concentrated solution of oxidizer salt, such as an aqueous substantially saturated ammonium nitrate solution, from the tank 341 through line 342 and thence through valve 340 and line 435 into the fluid pump 339.

It will be understood in the system described above, that the master pump M supplies power for feeding the various dry and wet ingredients to a mixing zone whereas master pump M supplies power for mixing the ingredients and delivering them as a slurry to a point of use. It will be understood however, that various other arrangements could be used, e.g. with one or more master pumps applying the necessary motive force for any or all of the various fluid motors which operate the mechanical parts.

A comparison of the system of FIG. 9 with the apparatus previously described shows that this is essentially an alternative system for accomplishing the same general results in substantially the same manner as has been described above in detail.

It will be obvious that other variations and modifications may be made in the method and in the various embodiments of apparatus described above. Various features of the several modifications described may be inter- 14 changed also, as would readily occur to those skilled in the art. It is desired and intended, by the claims below, to cover these and such other variations and changes as would suggest themselves to those familiar with the art, as broadly as the prior art properly permits.

What is claimed is:

1. A system for preparing and delivering pumpable explosive slurries of suspended solid particles in a liquid solution of oxidizer, which comprises, in combination, a mixing zone, a means for holding a supply of said particles, positively driven metering means for delivering said particles to said zone from said supply at a controlled rate, means for selectively varying said metering rate, a tank for liquid, selectively variable means for delivering liquid from said tank to said zone at a comtrolled rate, mixing means in said zone to form said particles and said liquid into a pumpable slurry, slurry pump means for taking said slurry from said mixing zone to a point of delivery, and a recycle connection between the slurry pump and a conduit leading towards said slurry pump, said system including selectively controllable means for varying the delivery rate of said, slurry pump.

2. Combination according to claim 1 wherein a single drive element supplies driving power simultaneously and selectively to said particle metering means, said liquid delivering means and said slurry pump means.

3. Combination according to claim 2 wherein a prime mover drives a jack shaft directly and said jack shaft drives the metering means, liquid delivering means and pump means directly.

4. Combination according to claim 1 wherein the mixing means and the slurry pump are interconnected to insure operation of each whenever the other is operated independently of the operation of other parts.

5. Combination according to claim 1 comprising a recycle connection at the slurry pump which is variably controllable to vary the inventory of slurry in the mixing zone, thereby to control the time and degree of slurry mixing.

6. Combination according to claim 1 wherein the mixing means comprises a plurality of rotating bars movable between fixed bars to facilitate rapid formation of smooth, homogeneous explosive slurry with safety.

7. Combination according to claim 6 wherein the mixing means provides suflicient shear of said slurry to incorporate substantial aeration therein.

8. Combination according to claim 1 which includes an air compressor and an air storage tank.

9. Combination according to claim 8 which includes an air operated clutch for driving the particle metering means.

10. Combination according to claim 1 which includes a fluid pump as a prime mover, fluid flow lines for the pumped fluid, and separate motors operable by said pumped fluid for driving respectively the particle metering means, the liquid delivery means and the slurry pump.

11. Combination according to claim 10 which includes means for automatically timing the operation of the metering means and the liquid delivery means.

12. Combination according to claim 1 which comprises a means for supplying a stream of water under pressure in addition to said liquid delivering means.

13. Combination according to claim 1 which comprises a plurality of said particle metering means, and means for variably controlling the respective delivery rates of said plural metering means to vary the proportions of diflerent particulate materials in the slurry.

14. Combination according to claim 1 which comprises means for removing fine dust from the mixing zone.

15. The method of preparing an explosive slurry comprised of a liquid containing oxidizer in solution and containing also undissolved suspended particles which are sufliciently reactive with said oxidizer to cause the slurry to explode powerfully when detonated, said method comprising the steps of positively metering said particles at a selectively controlled rate, and delivering said liquid also at a selectively controlled rate to a mixing station, including a delayed action thickener material for said liquid in the slurry, mixing the liquid and the particles to form a smooth slurry in said station, withdrawing slurry in a stream from said station and pumping it to a delivery point, and controlling both the inventory in the mixing station and the slurry delivery rate by recycling a selected portion of said withdrawn slurry stream, thereby to control physical properties of the slurry.

16. Method according to claim 15 wherein aeration of the slurry is augmented by said recycling.

17. Method according to claim 15 which also comprises the step of homogenizing the slurry by substantial shear mixing before it is finally pumped to the delivery point.

18. Method according to claim 15 which comprises forcibly pumping a circulating driving fluid through a cycle and carrying out the metering and pumping steps by the driving action of said circulating fluid.

19. Method according to claim 15 which comprises mixing the liquid and the particles together simultaneously with the slurry delivery, and separately controlling the flow of the liquid and particulate ingredients to the mixing stage so that build-up of deposits in said mixing stage is substantially prevented.

20. Method according to claim 15 which includes substantially simultaneous and continuous mixing and slurry delivery While the supply of ingredients is independently controlled, and wherein the supply of particulate solids is commenced after the mixing and delivery operations are initiated.

21. Method according to claim 15 wherein the mixing operation is conducted with sufficient vigor and shear to incorporate a substantial number of small air bubbles in the slurry, thereby to reduce its density to a controlled degree.

References Cited UNITED STATES PATENTS 3,303,738 2/1967 Clay et a1 86-l X 3,380,333 4/1968 Clay et al. 86-20 3,465,675 9/1969 Bronstein, Jr. 102-23 SAMUEL FEINBERG, Primary Examiner J. I. DEVITT, Assistant Examiner US. Cl. X.R. 102-23 

